Direct writing recorder



Aug. 23, .1960 J. R. KELLEY DIRECT WRITING RECORDER Filed Jan. 10, i958 3 Sheets-Sheet 1 INVENT OR. I JOHN R. KELLEY ATTORNEKJ' Aug. 23, 1960 J. R. KELLEY 2,950,162

DIRECT WRITING RECORDER Filed Jan. 10. 1958 I I 221 f' INVENT OR.

JOHN R. K511i) 4 TTORNE )4! FIG. 2.

3 Sheets-Sheet 2 Aug. 23, 1960 J. R. KELLEY DIRECT WRITING RECORDER 3 Sheets-Sheet 3 Filed Jan. 10, 1958 United States Patent DIRECT WRITING RECORDER John R. Kelley, Sierra Madre, Califl, assignor to Bell & Howell Company, Chicago, Ill., a corporation of Illinois Filed Jan. 10, 1958, Ser. No. 708,263

7 Claims. (Cl. 346-74) This invention relates to direct writing recorders.

Although the invention has many applications, it is particularly suitable for use in direct writing string galvanometers, and it is described in detail below in connection with such application.

In a typical string galvanometer, the writing element is an elongated movable conductor or string supported at its two ends so that its central portion can be deflected transversely a relatively large distance in either of two directions to provide the large amplitudes of motion which are required for recording directly.

The writing element lies in a magnetic field perpendicular to the length of the string, so that the string or writing element moves transversely with respect to the magnetic flux in accordance with the magnitude of the electric current which flows through it in response to an applied signal.

Preferably, the string is supported at each end by springs so that as the string is deflected in either direction, the springs permit the ends of the string to move closer together.

For direct writing on current-sensitive recording paper, an anvil having an edge located at the central portion of the string is employed to guide the recording paper adjacent the center of the string. The edge of the anvil is perpendicular to the string, and the current-sensitive paper is moved over the edge of the anvil so that it passes between the anvil and the string. Suitable means are provided for urging the string against the paper where the paper passes over the edge of the anvil, and a source of current is coupled between the paper and the string so that an electric current passes between the paper and the string at the intersection of the string and the line formed where the recording paper passes over the edge of the anvil. The current density at the point of contact between the paper and the string is sufliciently high to turn the paper black at that point. Thus, a trace is formed on the paper which provides a record of the deflections of the string in response to an applied signal.

The disadvantage of the conventional arrangement just described is that the writing element or string has to slide directly on the relatively rough surface of the recording paper, and due to the relatively high coefficient of friction between the element and the paper, some sensitivity is lost. Also, many types of recording paper have carbon or other material deposited on their sensitive surfaces, and the material coats the string, further increasing friction between the string and paper, and adversely affecting the quality of the record.

This invention provides an improvement which eliminates the sliding of the writing element directly on the recording paper and prevents carbon from collecting on the writing element. Moreover, the frictional forces on the writing element are reduced, thereby improving the sensitivity of the galvanometer.

Briefly, the invention contemplates apparatus for direct recording of a signal on an electro-sensitive paper com- ICC 2 prising a signal transfer block having a plurality of conductors mounted on it and insulated from each other. An electrically conductive Writing element is disposed adjacent the conductors and means are provided for moving the writing element into electrical contact with successive conductors in accordance with the strength of the signal to be recorded. Means are provided for holding the paper in contact with the conductors, and means are also provided for imposing a writing voltage between the writing element and the paper so that the paper is marked in accordance with which conductor on the transfer block the writing element is in contact.

Preferably, the signal transfer block is of an insulating material and has a smooth surface which is flush with a respective portion of each of the conductors. The writing element is an elongated conductor or wire adapted to slide smoothly over the smooth surface of the signal transfer block, thereby making successive contact with different conductors.

These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic elevation of a direct recording oscillograph using the invention;

Fig. 2 is a view taken on line 2-2 of Fig. 1;

Fig. 3 is a perspective view of the first step in manufacturing the signal transfer block shown in Figs. 1 and 2;

Fig. 4 is a perspective view of the second stage of the manufacture of the transfer block;

Fig. 5 is a perspective view of the signal transfer block in the third state of its assembly;

Fig. 6 is a perspective view of the completed transfer block;

Fig. 7 is a schematic perspective view of an alternate embodiment of a transfer block made in accordance with this invention to record two signals simultaneously;

Fig. 8 is a schematic sectional view of a signal transfer block made in accordance with this invention to provide an amplified or compressed record of the movement of a writing element; and

Fig. 9 is a schematic perspective view of a signal transfer block made in accordance with this invention to pro vide a linear recording of a curvilinear movement of the writing element, or vice versa.

Referring to Fig. 1, a typical direct writing oscillograph 12 includes an electrically conductive elongated writing element or string 14 mounted at its opposite ends on cantilever springs 16 each supported on an electrically insulating bracket 17 in a respective opening 18 in a magnet 19. The magnet includes a relatively long north pole piece 20 underneath the string and a pair of longitudinally spaced 'south pole pieces 22 above the string and connected at their respective outer ends to the north pole piece by yokes 24. The lower edge 25 of an elongated transfer block 26 bears down against the central portion of the string in the gap between the two south pole pieces of the magnet. A strip of electro-sensitive recording paper 28 passes from a supply roller 29 over a first guide roller 30, down around a second guide roller 32, up over a flat surface 33 of the signal transfer block, over a third guide roller 34 and on to a storage reel 36. As can be seen in Fig. 1, the second guide roller 32 is set to hold the paper in contact with the flat surface 33 of the signal transfer block.

The signal to be recorded comes from a signal source 40, through an amplifier 42, and through the writing element or string. The signal causes the string to be deflected to the right or left (as viewed in Fig. 2) by an amount proportional to the strength of the signal. Thus, when the signal is zero, the string is at the center position shown in Fig. 2. When the signal is at a maximum, the string moves to the extreme right or left of the lower surface of the signal transfer block, depending on the signal polarity. A writing current or voltage is supplied from a writing current source 44 to the string and paper through leads 45 and,46, respectively. A commutator 47 on the end of the lead 46 remote from the writing current source makes a sliding contact with guide roller 34 to effect electrical contact with the recording paper.

The detailed construction of the signal transfer block and its method of manufacture is shown in Figs. 3 through 6. Referring to Fig. 3, a conductive wire 48 is wound around an elongated core 50 of triangular cross section. Preferably, the core is made of an insulating plastic, such as one of the Well known epoxy resins. The wire can be of any desirable size and wound on the core with any suitable spacing between adjacent coils of wire. The smaller the wire and the closer the spacing of adjacent coils, the more detailed the recording properties of the signal transfer block. For ordinary oscillography, the wire can be approximately .001 inch in diameter with a spacing of about .001 inch between adjacent coils. After the core is completely wound it is placed in a cylindrical mold (not shown) and potted in more epoxy resin so that the triangular core and wire are completely encapsulated in a cylindrical cover 52 as shown in Fig. 4.

Referring to Fig. 5, the flat surface 33 is cut the length of the cylinder until the wire loops 56 at one corner of the triangular mold are exposed and flush with the surface of the plastic. Preferably the surface is polished to provide a minimum of frictional resistance.

Referring to Fig. 6, a relatively deep longitudinal cut 58 is made along the cylinder at one of the other corners of the triangular core so that each coil of wire is cut to leave a pair of exposed ends flush in a second smooth flat surface 60 formed by the cut 58. A second longitudinal cut 62 is made on the cylinder at an angle to cut 58 so that the two cuts 58 and 62 intersect in the edge 25 which contains one set of exposed wire ends. The edge 25 is formed so the exposed Wire ends are flush with the surface of the plastic. The other set of exposed wire ends are covered either by an insulating tape 64 or a coating (not shown) of additional plastic or lacquer. Thus, each coil of wire is separated from the adjacent coils and provides an insulated electrical conductor from the smooth fiat surface of the signal transfer block to the straight edge in which the exposed wire ends lie.

The signal transfer block is mounted in the apparatus shown in Figs. 1 and 2 so that the string bears against the edge of the block containing the exposed wire ends and so that the paper slides over the fiat surface with the exposed wire loops.

The operation of the apparatus shown in Figs. 1 and 2 is as follows:

When an oscillograph recording is to be made, the writing current is turned on, and the take-up reel 36 is turned on so that recording paper is moved through the system as indicated by the arrow in Fig. l to be in contact with the exposed wire loops in the flat surface 33 of the signal transfer block. As long as there is no signal, the writing element or string remains at the center position shown in Fig. 2, contacting a corresponding conductor in the signal transfer block which in turn causes a straight trace 66 to be made on the paper as it moves past the transfer block. As signals of various strength and polarity are passed through the string, the string is deflected to the right or left, successively making contact with different conductors in the signal transfer block in accordance with the strength and polarity of the applied signal. As the string moves back and forth over the various wire loops, a corresponding trace is made on the recording paper.

The advantage of this invention is that the string or recording element slides on a polished smooth surface which offers relatively little frictional drag to the 3. string as compared to the conventional system in which the string is in direct contact with the recording paper. In addition, the string does not pick up carbon or other material from the paper.

Fig. 7 shows an alternate embodiment of the invention in which a signal transfer block 68 is used for dual string operation. In the arrangement shown in Fig. 7, the signal transfer block is a laminated structure of thin pieces of metal 70 sandwiched between and bonded together by insulating layers of plastic 72;. The signal transfer block includes an upper smooth edge 74 on which an upper or first string 76 is adapted to slide. A second or lower string 78 is mounted to slide along a second or bottom smooth edge 80 on the block. A smooth side edge 82 of the signal transfer block makes sliding contact with a strip of recording paper 84 carried over a guide roller 86. Each of the strings shown in Fig. 7 lie in a magnetic field and are adapted to receive a writing voltage and a respective signal as described for the apparatus shown in Figs. 1 and 2. The advantage of the apparatus shown in Fig. 7 is that a dual record can be recorded on the same area of a single piece of recording paper, which has not been possible with previously available conventional equipment.

Fig. 8 shows another embodiment of the invention in which a signal transfer block 87 is adapted to effect amplification or compression, depending on which way it is used, of the movement of a writing element. For the purpose of explanation of the signal transfer block of Fig. 8, it is assumed that the block is to be used to provide an amplified record of the movement of a writing element 88 adapted to move through a maximum amplitude of distance indicated by X in Fig. 8. A plurality of upwardly and outwardly extending conductors 90 terminate in the smooth bottom face 91 of a body 92 of insulating plastic, and also terminate in a smooth upper surface 93 of the body over which rides a strip of recording paper 94 on a roller 95. The spacing between adjacent conductors is greater at their upper ends than their lower ends by a factor N, which is the amplification factor for the signal transfer block. Thus, as the string moves a distance X, the recorded trace on the paper moves a distance NX. If the recorded movement of the string is to be compressed instead of amplified, the position of the paper and writing element are reversed.

With the signal transfer block 96 shown in Fig. 9, a plurality of upright parallel conductors 97 embedded in a body of plastic 98 terminate at their lower ends flush with the straight bottom edge of the block which is in contact with a strip of recording paper 99 carried over a guide roller 100. The upper ends of the conductors terminate in a smooth semi-circular concave surface 101 having a radius of curvature R centered at point P. An elongated writing element 102 is pivotally mounted at one end at point P so that its outer end with a contact element 103 slides along the curved surface of the signal transfer block. The movement of the writing element 102 can be actuated by any suitable means. For example, the pivoted end may be attached to a movable coil of a conventional galvanometer. Thus, the circular movement of the coil and writing element is transformed into a linear movement on the recording paper. A converse eifect can be obtained, i.e., converting a linear movement to a curved recording, by arranging the paper to fit the curved surface of the signal transfer block and using a linear movement type of string as previously described in contact with the bottom edge of the signal transfer block.

lclaim:

1. Apparatus for direct recording of a signal on an electr c-sensitive paper, the apparatus comprising a body, a plurality of conductors mounted on the body and insulated from each other, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors. in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors, and means for imposing a writing voltage between the writing element and the paper.

2. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body, a plurality of conductors mounted on the body and insulated from each other, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors, means for imposing a writing voltage between the writing element and the paper, and means for moving the paper with respect to the block.

3. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body having a smooth surface, a plurality of conductors insulated from each other and mounted on the body to lie flush in the smooth surface, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors in the smooth surface in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors, and means for imposing a writing voltage between the writing element and the paper.

4. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body, a plurality of conductors mounted on the body and insulated from each other, an elongated electrically conductive writing element, means for supporting the writing element to permit it to be in contact with the body and be deflected transversely along the body to contact successive conductors, means for establishing a magnetic flux transverse to the writing element, means for applying the signal to the writing element to deflect it in the magnetic field and cause it to slide on the body and contact successive conductors in accordance with the strength of the signal, means for holding the paper in contact with the conductors, and means for imposing a writing voltage between the writing element and the paper.

5. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body of electrically insulating material, a plurality of separate conductors wound on the body and spaced from each other, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors, and means for imposing a writ ing voltage between the writing element and the paper.

6. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body, a plurality of conductors mounted on the body and insulated from each other, the conductors being closer together at one portion of the body than at another, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors at one portion of the body in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors at another portion of the body, means for imposing a writing voltage between the writing element and the paper, and means for moving the paper with respect to the body so a trace of the signal is formed on the paper.

7. Apparatus for direct recording of a signal on an electro-sensitive paper, the apparatus comprising a body, a plurality of conductors mounted on the body and insulated from each other, the body having a curvilinear surface with which one portion of each conductor is flush, and having a flat surface with which another portion of each conductor is flush, an electrically conductive writing element, means for moving the element into electrical contact with successive conductors in one of the surfaces in accordance with the strength of the signal to be recorded, means for holding the paper in contact with the conductors in the other surface, and means from imposing a writing voltage between the writing element and the paper.

References Cited in the file of this patent UNITED STATES PATENTS 

